The androgen receptor (“AR”) is a ligand-activated transcriptional regulatory protein that mediates induction of male sexual development and function through its activity with endogenous androgens. Androgenic steroids play an important role in many physiologic processes, including the development and maintenance of male sexual characteristics such as muscle and bone mass, prostate growth, spermatogenesis, and the male hair pattern. The endogenous steroidal androgens include testosterone and dihydrotestosterone (“DHT”). Steroidal ligands which bind the AR and act as androgens (e.g. testosterone enanthate) or as antiandrogens (e.g. cyproterone acetate) have been known for many years and are used clinically.
6-[(4R)-4-Methyl-1,1-dioxido-1,2,6-thiadiazinan-2-yl]isoquinoline-1-carbonitrile (Formula I), in its free base form, has the chemical formula C14H14N4SO2 and the following structural formula:

Synthesis of 6-[(4R)-4-methyl-1,1-dioxido-1,2,6-thiadiazinan-2-yl]isoquinoline-1-carbonitrile is disclosed in co-pending international patent application, PCT/IB2013/060381, filed 25 Nov. 2013, and published as WO 2014/087298 on 12 Jun. 2014, assigned to the assignee of the present invention and which is incorporated herein by reference in its entirety. 6-[(4R)-4-Methyl-1,1-dioxido-1,2,6-thiadiazinan-2-yl]isoquinoline-1-carbonitrile is known to be active as a selective androgen receptor modulator (SARM) and, as such, is useful for treating and/or preventing a variety of hormone-related conditions, for example, conditions associated with androgen decline, such as, inter alia, anaemia; anorexia; arthritis; bone disease; musculoskeletal impairment; cachexia; frailty; age-related functional decline in the elderly; growth hormone deficiency; hematopoietic disorders; hormone replacement; loss of muscle strength and/or function; muscular dystrophies; muscle loss following surgery; muscular atrophy; neurodegenerative disease; neuromuscular disease; obesity; osteoporosis; and, muscle wasting.
Identification of new solid forms of a known pharmaceutical active ingredient provide a means of optimising either the physicochemical, stability, manufacturability and/or bioperformance characteristics of the active pharmaceutical ingredient without modifying its chemical structure. Based on a chemical structure, one cannot predict with any degree of certainty whether a compound will crystallise, under what conditions it will crystallise, or the solid state structure of any of those crystalline forms. The specific solid form chosen for drug development can have dramatic influence on the properties of the drug product. The selection of a suitable solid form is partially dictated by yield, rate and quantity of the crystalline structure. In addition, hygroscopicity, stability, solubility and the process profile of the solid form such as compressibility, powder flow and density are important considerations.
As such, there is a need to identify solid forms of 6-[(4R)-4-methyl-1,1-dioxido-1,2,6-thiadiazinan-2-yl]isoquinoline-1-carbonitrile that exhibit acceptable physicochemical, stability, manufacturability and/or bioperformance properties.